This invention relates to a controlled-phase R.F. system comprising an input port, an output port, an R.F. amplifier for amplifying an R.F. signal supplied to the input port so as to provide a net gain greater than unity at the output port relative to the input port, a phase-shifter for introducing a controllable phase shift between the input port and the output port, and phase-control means comprising means for detecting a difference between the phase at the output port relative to the phase at the input port and an operational reference relative phase formed within the system, and for controlling the phase-shifter so as to tend to minimise said difference.
Such a system is known from U.K. Patent Specification No. 1 246 209. In this known system, the phase-difference detecting means comprises a phase quadrature detector, and the system is thus adapted to tend to maintain, substantially constant, a phase shift between the input port and the output port that has a single predetermined value corresponding to the condition of phase quadrature at the inputs of the phase detector.
It is desirable to provide an R.F. amplifier system which can give more than one value of substantially constant phase at the output port relative to the input port, particularly for use with a phased antenna array. When such an array is used for transmission, it is necessary to be able to control the respective phases of the R.F. energy supplied to each antenna element of the array relative to one another, and to be able to select each of the respective phases from a plurality of different values. It is an object of the invention to provide such a system.